An important feature of uplink transmission is that different user equipment devices (UEs) perform orthogonal multiple access on a time-frequency resource. Specifically, different UEs from a same cell perform uplink transmission without interfering with each other. To ensure uplink transmission orthogonality and avoid intra-cell interference, it is required that time at which signals from different UEs reach a base station is aligned. The base station can correctly decode uplink data sent by the UE, provided that the base station receives the uplink data within a cyclic prefix (CP) range. Therefore, uplink synchronization requires that time at which signals of different UEs from a same subframe reach the base station falls within the CP.
Ultra-reliable and low latency communications (URLLC) is a communication scenario proposed for fifth generation (5G) mobile communication systems. In the URLLC scenario, there is a tough requirement for data transmission reliability and data transmission latency. For example, a latency of an uplink user plane or a downlink user plane cannot exceed 0.5 millisecond (ms), and a bit error rate within 1 ms cannot exceed 0.0001%. Existing uplink synchronization methods for sending uplink information cannot meet the requirements of the 5G mobile communication systems.